Re: Clarification on HPACK dynamic table size increases?

Hervé Ruellan <herve.ruellan@crf.canon.fr> Tue, 17 March 2015 14:35 UTC

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Date: Tue, 17 Mar 2015 15:31:02 +0100
From: Hervé Ruellan <herve.ruellan@crf.canon.fr>
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Subject: Re: Clarification on HPACK dynamic table size increases?
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On 03/13/2015 12:49 AM, Mike Bishop wrote:
> 6.3 isn't saying that the value can only be reduced.  There is a maximum that the decompressor has said it's willing to allow the compressor, and the compressor is allowed to choose any value <= what the decompressor allows it.  The wording there could be cleaner, since there's a maximum table size, and a maximum value *for* the maximum table size.  :-(
>
> -----Original Message-----
> From: Daurnimator [mailto:quae@daurnimator.com]
> Sent: Thursday, March 12, 2015 3:53 PM
> To: ietf-http-wg@w3.org
> Subject: Clarification on HPACK dynamic table size increases?
>
> I'm working on implementing HPACK, wanted clarification on whether the dynamic table can grow:
>
>>From 4.2
>> This mechanism can be used to completely clear entries from the dynamic table by setting a maximum size of 0, which can subsequently be restored.
>
> However, 6.3 has a MUST that the table may only be reduced in size:
>> The new maximum size MUST be lower than or equal to the last value of the maximum size of the dynamic table.
>
>
> Regards,
> Daurn.
>

I agree that 4.2 isn't very clear, and that 6.3 is misleading. I just 
created a pull request for correcting 6.3:
https://github.com/http2/http2-spec/pull/729

Hervé.